Multiband tv-fm antenna



Oct. 13, 1970 N. J. REA

MULTIBAND TV-FM ANTENNA 7 Sheets-Sheet 1 Filed April 20, 1967 nv vEm'aeIVORMAIV .Z IPA-A 5W ATTORNEYS.

Oct. 13, 1970 N. J. REA

MULTIBAND TV-FM ANTENNA 7 Sheets-Sheet 5 Filed April 20. 1967 I IVVE/VI'OQ A QRMAN J: REA

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MULTIBAND TV-FM ANTENNA 7 Sheets-Sheet 4 Filed April 20, 1967 INVENTORNORMAN .1. REA

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MULTIBAND TV-FM ANTENNA Filed April 20. 1967 7 Sheets-Sheet 5 7 2 .92 ifQ L IN VfN 7'02 NORMAN J. REA

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MULTIBAND TV-FM ANTENNA Filed April 20, 1967 7 Sheets-Sheet '7 200 J M wQ=.

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NORMAN J- P54 A TTOENEYS United States Patent US. Cl. 343-7925 9 ClaimsABSTRACT OF THE DISCLOSURE A multiband TV-FM periodic antenna isprovided in which the front element has an extending hairpin-likesection, capacitatively coupled thereto. In operation, the eX- tendingsection is unconnected at low band frequencies but effectively connectedat the high band frequencies.

This application relates to a multiband antenna of the backward wavetype and more particularly relates to an antenna for VHF television andFM radio reception. Specifically, this invention relates to a periodicmultidipole antenna which is effective for all VHF television and FMradio reception.

This invention also relates to an interlaced VHF-UHF television and FMradio antenna.

It has been common to provide multiband antennas by providing pluralantennas mounted on the same mast, essentially in cascade. For example,a mast could carry a first antenna section designed for the low-bandchannels 2-6; a second antenna designed for the high-band channels 7-13;and a third antenna designed for FM band. Such antennas require manyelements, are inherently inefficient and are expensive.

Problems have existed in devising a multiband interlaced antennaeffective for the VHF-TV and FM bands. It has been found experimentally,that a periodic antenna for all TV and PM will encounter problems ofhigh side lobes, poor impedance matching characteristics, and reducedgain for certain of the frequencies. These problems become accentuatedwhen the antenna is used for color TV reception.

In explaining the problems encountered in the operation of my antenna,the following considerations are helpful, but in general are onlyreasonable approximations of the true performance, particularly asapplied to periodic antennas.

When an antenna is used only for the low and high bands of VHF, thefrequency ranges to be covered are 54-88 mc. (channels 26) and 174-216(channels 7-13) and 88-108 (FM). It will be apparent that antenna dipoleelemets cut as half-wave elements (total length) at 88 me. will act as afull-wave element at 174 me.

Consider now the performance at the low end of the high band (channel 7,174 me.) when the low band is extended to include FM to 108 mc. Antennadipole elements cut as half-wave elements (total length) at 108 mc. willact as having a length between a half and a full wave, at 174 mc. andadjacent frequencies, and not as a resonant element. Therefore, in thelow end of the high band (174 mc.), substantial problems of high sidelobes, impedance mismatch and changing phase centers occur. Thisproduces incorrect and distorted colors, ghosts, and in general, poorreception when what is required for high quality FM and color receptionis just the opposite.

In the periodic antenna, if the first element is poorly matched to theincoming signal at selected frequencies, such as 174 mc., severe patternbreakup occurs. The aforementioned multiple side lobes and varying phasecenters result along with undesirable harmonics, reducing the ice gain,causing ghosts and generally increasing the distortion.

In my invention, I have provided a means for increasing the totaleffective dipole lengths of one or more of the antenna elements whichpresent undersirable harmonics so as to neutralize the undesired effectsand eliminating pattern breakup.

An object of my invention is to provide a multiband interlaced antennafor FM and TV.

A further object of my invention is to provide a multiband parasiticdirector.

Another object of my invention is to provide an antenna elementoperative at a first range of frequencies, and being relatively inert ata second higher range of frequencies.

A further object of my invention is to provide an improved periodicantenna for multiband use.

Still another object of the invention is to provide an improvedparasitic array of director elements.

A still further object of this invention is to provide a multiband TVand FM antenna in which the component elements function in all bands.

Yet another object of this invention is to provide a multiband, trimodalantenna for the VHF, UHF TV bands, and the FM band.

Briefly, in my invention, I provide an array of spaced parallel dipoles,of the general periodic type, each having a length of predeterminedratio to the preceding dipole, the longest dipole being proportioned toresonate at channel 2. The array tapers with shorter dipoles for variouschannels including channel 13 and for FM radio band reception. In anaspect of the invention, the active elements are equally spaced one fromthe other.

The front active element has an associated extension element, parallelthereto, which is substantially uncoupled or unconnected at the lowband, but becomes coupled at the high band to increase the effectivelength. That is, the extensions are capacitatively coupled, theimpedance of such coupling being an effective short circlit at the highband. The total dipole length is increased by an amount so that thefront element becomes relatively inert and does not cause patternbreakup and the related effects mentioned before.

I further provide a parasitic director array of elements which arevariably spaced apart, the outer ones being further spaced apart thanthe inner ones. It is known that in the operation of log periodicdipoles, slow traveling waves are present. Slow waves are waves whoseapparent or phase velocity is less than that of free space. In mydirector array, the velocity of the wave is gradually slowed as itreaches the active elements and less energy is lost.

The parasitic array comprises elements of equal length; however, eachelement has a unique associated parallel extension, which allows theelements to operate effectively in the low and high bands.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will best be understood by reference to the following descriptionof embodiments of the invention taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a perspective view of one embodiment of the antenna array ofthis invention;

FIG. 2 is a top diagrammatic view of the antenna of FIG. 1;

FIG. 3 is a front view, partly in section of the first driven antennaelement of the array;

FIG. 4 is a side sectional view along 4-4 of FIG. 3;

FIG. 4A is a perspective view showing further detail of a supportinginsulator and takeoff terminals;

FIG. is a side sectional view of the bimodal parasitic director element;

FIG. 6 is a schematic diagram of the bimodal director element;

FIGS. 6A, 6B and 6C are diagrams of the current distribution in thebimodal director element for low and high band;

FIG. 7 is a diagram of an embodiment of my invention having amultidirector system;

FIG. 8 is a top view of a multi-element parasitic section;

FIG. 9 is a top view of another embodiment of my invention for use alsoin UHF;

FIG. 10 is a schematic diagram of another embodiment for use also in UHFillustrating the current distribution.

THE ACTIVE ARRAY Referring now to FIG. 1, there is shown a mast 10supporting a conductive cross arm 11 on which the active array 100 andthe parasitic elements 40, 40' are mounted. The active array comprisesdipole elements 20, 30, 30', 32, 32, 34, 34', 36, 36 and feed wires 12,13. As shown in more detail in FIGS. 2 and 3, the dipole 20, 20comprises dipole rods 21 and 21A, and identical extension elements 22and 22A. Extension 22 comprises an elongated thin rod bent back uponitself to form generally a hairpin (FIG. 3). The extension is attachedto the dipole element by a pair of triangularly-shaped insulators 50(see FIG. 4) which have grooves 51 to accommodate the dipole element 21and the rod ends 22 in a resilient fit.

Rod 22 extends approximately 6 inches (Dimension W) beyond the end ofthe dipole in one preferred embodiment (FIG. 3). At for example, 174mc., the total effective length of each active arm is /2 wavelength andthe total antenna length is 1 wavelength. The various dimensions of thedriven element for the preferred embodiments (assembly 1) are shown inthe drawing, FIGS. 2 and 3, as dimensions X, Y and Z, and are listedbelow. Since other embodiments may also be used, typical dimensions arealso included (assemblies 2 and 3).

There is also shown an end grounding strap 14, FIG. 2, which is commonto all of the antennas, which grounds the driven dipoles and providesdirect connection to the cross arm to bleed noise and static charges.

Referring now to FIG. 2, it will be seen that the elements 20, 30, 32,34, 36 increase in length, each one bearing a predetermined ratio to thepreceding one. It will also be observed that each of the dipole elements20, 30, 32, 34, 36 is equally spaced from the next successive element.

The operation of my invention may be briefly described here. The theoryby which my antenna operates has not been firmly established; however,it is my belief that by providing a dipole structure, the length of eachsuccessive dipole varying periodically and yet providing equally spaceddipoles, I have provided a structure in which undesired side lobes fromsuccessive elements tend to cancel each other out. It was alsodiscovered that a spacing of 12%. between successive parallel, dipoleelements provided an interference radiation relationship whichsubstantially cancelled the side lobe levels inherent in the individualdipole patterns at the high band frequencies. This eliminates the Vrequirement or the parasitic stubs used in other devices.

MECHANICAL CONSTRUCTION The mechanical constructionis illustrated inmore detail in FIGS. 3, 4 and 4A. The cross arm 11 is square 4 shapedand supports a series of arcuate-shaped insulators 60 which support thedipole elements as well as providing the electrical connections betweensuccessive pairs of dipole elements, as will be desribed. All of theinsulators have the same construction and only one will be describedbriefly, it being understood that a pair of insulators are mounted aboveand below the mast for each pair of dipoles. Insulator 60 is generallyL-shaped and has a fiat horizontal section 61 except for a small recessto accommodate the cross arm 11 and a vertical section 63.

The dipole rod 21 is fitted into a hollow metal receiv ing socket 23having a generally square exterior contour held between two opposingflat sections 61 and has a pin 62 extending therethrough, allowingrotation. Each dipole element is thus pivotally mounted so as to rotatein the horizontal plane containing all of the dipole elements. Thisrotation feature is desirable to provide easy packing and mounting ofthe antenna.

There is provided a spring clip 75 having a wedged aperture 76 (FIG. 4A)of approximately the same dimensions as the dipole socket. The clip isheld by opposing flat sections 61.

Each insulator has a groove 64 in a slightly extending section 65 tosupport the wires 12, 13. Each of the insulators has narrow slots 66extending within the arcuate portion of the insulator, each containing aconductive strip 66A, 66B (FIGS. 3, 4A) to provide the contact betweenthe wire 12 of the dipole socket 23 and pin 62. Although not shown, aconductive wall may be provided in groove 64 to present a firmelectrical contact between the internal conductor 66 of the insulatorand the feed wire.

The arcuate conductive strips 66A, 66B (FIG. 3) are located on oppositequadrants of the circle defined by the two insulators; these quadrantsalternate with respect to successive elements so that dipole element 21is connected to the feed wire 12 which in turn is connected to element30, then to 32, then to 34' and finally to 36, while the other feed wire13 is connected to dipole elements 20', 30, 32', 34, 36, to providesuccessive feeds in opposing phase relation.

Takeoff terminals are shown at 68 having fastening screws 69. A metallicfitting 70 connects the terminals to the feed wire lines. A matchingtransformer 71 (FIG. 4A) for 75 ohm operation may be optionally usedwhen coaxial lead-in is employed.

THE DIRECTOR ARRAY The director 40 is shown also in more detail in FIG.5 and it will be understood that more than one director may be utilizedas shown in FIG. 8. The director support is mechanically similar to thesupports for the active dipoles and uses the same arcuate-shaped plasticinsulators Which serve as brackets, except that internal conductors arenot required.

The director is bimodal and has associated with it a stub also in theshape of an elongated wire being bent upon itself to define parallelarms 81 and 82 and a bight section 83. In this embodiment the arm 81 islonger than the arm 82. The stub is mechanically fastened to thedirector rod or tube by triangularly-shaped insulators of the samecharacteristics as the insulators 50 shown and described in connectionwith FIGS. 3 and 4. One arm 82 of the extension is directly connected tothe director rod by a shorting clip 92.

The relative dimensions V, W, X, Y, Z are shown in the drawing, FIG. 5.For one embodiment, typical dimensions are as follows:

The bimodal director of FIG. is diagrammatically illustrated in FIG. 6and operates essentially as a colinear element. There is shown thedirector as comprising three essential sections, the main section L, theextending section M, and the intermediate section N. The position of theshorting stub is shown at 92 and 83 illustrates the bight section. FIG.6A is intended to illustrate the high band current distribution on thebimodal director element. In the case where the total length of thedirector element is a full-wave length, two half wave current componentsI1 and 12 will be induced. The current component I3 caused by theintermediate section N will be cancelled out by the component ofcurrents I4 and I5 provided by the induced currents in the overlappingpaths provided by the sections indicated at 40A (which produces 14) and80A (which produces I5).

FIG. 6B illustrates the resulting current distribution at highbandderived from the analysis of FIG. 6A.

FIG. 60 illustrates the low band current distribution. In this mode ofoperation, element 80 is effectively a half wave length.

These are illustrations only of the principle disclosed herein of havingthe length of the active and director elements increased so as to avoidpattern breakup.

Referring now to FIG. 7, there is shown an array of active elements 100and an array of director elements 160 comprising dipole pairs 161, 162,163, 164. Each of the dipole elements is constructed in the same manneras element 40 shown in FIGS. 2 and 5. However, in the array, eachdirector element on a respective side of the cross arm is spaced atgradually increasing amounts. The spacing is expanded towards the frontof the parasitic structure to increase the velocity to more nearly equalthat free space.

One embodiment of the parasitic array is shown in FIG. 8 and comprisesseven dipole pairs 171, 172, 173, 174, 175, 176, 177. The relativespacing between successive elements is shown on the drawing and isrepeated here:

Parasitic elements: Spacing, inches TRIMODAL OPERATION FIG. 9 shows anembodiment of an antenna also operative for the UHF band, while FIG. 10illustrates diagrammatically the director element for trimodaloperation. In FIG. 9, there is shown an active UHF dipole element 200having a length of 5 /2 inches for each arm. A director 210 and anactive dipole 202 are positioned before and after the element 200respectively.

The interlaced director embodiment is shown in FIG. 10. The directorelements 210, 210' and 210" (FIGS. 9, 10) are of the same form. In FIG.10, between the two elements 210', 210", is a UHF active dipolecomprising two rod elements 214 each cut to approximate half wave lengthUHF. The UHF element 214 does not interfere at all with operation at thelow or high TV bands.

While the principles of the invention have been described in connectionwith specific apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation tothe scope of the invention as set forth in the objects thereof and inthe accompanying claims.

What is claimed is:

1. A mutliband antenna for use in the TV and FM bands, said TV and FMbands including the 54-108, 174-216 mc. bands comprising:

an array of active dipole elements the length of successive elementsvarying according to a predetermined ratio, each element being equallyspaced from the preceding element,

means for feeding each of successive elements in opposing phaserelationship,

said first active dipole elements each having at least one physicallyand electrically spaced, capacitively coupled, substantially parallel,extension member mounted adjacent thereto,

and at least one parasitic director element mounted in front of theactive elements, said capacitively coupled element being disconnected inthe 54-108 mc. band.

2. The antenna of claim 1 in which a plurality of director elements aremounted parallel to each other to form a director array,

said director elements being variably spaced one from the other inprogressively increasing space sequence away from said active elements.

3. The antenna of claim 1, in which the elongated element includes ahairpin-shaped member having two parallel extending elements, connectedat one of their adjacent ends.

4. The antenna of claim 3 in which said director element includes atleast one elongated conductive element spaced adjacent and parallelthereto over a predetermined length thereof and extending beyond saidactive element and a conductive stub coupling said elongated anddirector element.

5. The antenna of claim 1 in which the effective length of each of thefirst active elements including the respective extension is /2 A atapproximately 174 mc., whereby the total dipole length of said firstactive dipole element is 1 A the impedance of the capacitive couplingbeing substantially minimal at 174 mc.

6. The antenna of claim 9 in which said first active dipole has a totallength of /2 A at 108 mc., and the longest dipole of said array beingresonant at 54 mc.

7. The antenna of claim 5 including an interlaced, colinear UHF activeelement.

8. In sub-combination, an antenna for use in the TV and FM bands, saidTV and FM bands including the 54-108, 174-216 mc. bands, including atleast one pair of active dipole antenna elements,

and at least one elongated electrically spaced but capacitively coupledconductive element physically spaced adjacent and parallel to saidactive element over a predetermined length and extending beyond saidactive element and supporting means closely supporting said elementadjacent to said extension, said capacitively coupled element beingelectrically disconnected in the 54108 mc. band.

9. The antenna of claim 8, in which the elongated element includes ahairpin-shaped member having two parallel extending elements, connectedat one of their adjacent ends.

References Cited UNITED STATES PATENTS 2,417,808 3/1947 Carter 343833 X2,598,005 5/1952 Lippit 343-815 X 2,622,197 12/1952 Cruser 343-8022,885,675 5/1959 Simon et a1. 343895 X 2,975,423 3/1961 Wells 343-833Re. 25,604 6/ 1964 Greenberg 343-7925 X FOREIGN PATENTS 229,354 9/ 1958Australia.

HERMAN KARL SAALBACH, Primary Examiner SAXFIELD CHATMON, JR., AssistantExaminer U.S. Cl. X.R. 343-802, 815, 812

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,534369 October 13, 1970 Norman J. Rea

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 6, line 36, claim reference numeral "9" should read Signed andsealed this 6th day of April 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, JR.

Attesting Officer Commissioner of Patents

